Studies directed toward the total synthesis of azaspiracid.: Construction of the C1-C19 carbon backbone and synthesis of the C10, C13 nonnatural transoidal bisspirocyclic ring system

The efficient entry to the C-1-C-19 carbon backbone of azaspiracid is outlined utilizing a key Julia coupling strategy. Spirocyclization of a C-12 sulfone substrate induced formation of the unprecedented. nonnatural transoidal bisspiroketal. Construction of the bisspirocyclic array at C-10 and C-13, in the absence of the C-12 sulfone, led to formation of the cisoidal orientation of the bisspirocycle, with the nonnatural stereochemistry at C-13. (C) 2001 Elsevier Science Ltd, All rights reserved.